Replacement for mercury tilt switch

[zevon8]

Hello everyone

Has anyone here had any luck with the non-mercury tilt switches? I am looking to replace a mecury in glass tilt switch, but I don't know how well the ball bearing or pendulum style switches last. The application is in a vehicle, so it will be subject to heavy vibration, and I am wondering how well the gold plated ball bearing types, or similar mechanical switches stand-up. The load is less than 1 amp, but the switch should have low on-state resistance, and not be a "one-shot" or low duty cycle design.

Any suggestions or ideas greatly appreciated.

( The move away from mercury is due to WEEE / ROHS component limitations )

 

[John Sorensen]

The one time I tried using a non-mercury tilt switch (ball style) it didn't work well at all. Poor contact; very erratic. I ended up going with a mercury switch instead, but potted the whole thing.

j.

 

[williB]

how about the ADXL series .?
they measure tilt.

**broken link removed**

 

[zevon8]

Thanks for the response! I have had a hard time getting decent info from the various makers of alternate switches, regarding bounce, durability, etc.

Like you, what I am doing now is placing a regular mercury in glass switch in a plastic 35mm film container, and filling it with silicone, then mounting the whole thing with nylon "P" clamps. I have to put a "contains mercury, dispose of properly" label on it. It works well, but kinda looks "home-made."

Somewhere there must be a workable solution? I wonder what the appliance makers have done?

-edit-

Thanks williB, you posted while I was replying. What I am looking for is a simple, up or down type position switch. Along the lines of the sensing if the car trunk lid is opened or closed, so a light gets turned off or on. The Analog Devices IC looks interesting, but probably would involve too much support circuitry.

 

[zevon8]

hmm... looking at my post, I may have confused the issue a bit.

What I am doing is not sensing a trunk lid, but sensing the position of some machinery on a vehicle. This machinery has 2 positions, "deployed" and "stowed," approximately 90 degrees difference in the positions. The vehicle operator cannot always see if the machine has fully reached either position while sitting in the cab. This sensor simply turns on a LED on the cab control panel to indicate the state of the equipment. The mechanisms and motors moving the equipment is self controlling, the operator just needs an indication of if things have happened or not after operating the machine.

Unfortunately, using a limit switch is not possible, due to the small size of the equipment being deployed, and various mechanical limitations.

Sorry for not explaining better
Thanks!

 

[williB]

how about the ADXL series .?
they measure tilt.

**broken link removed**

 

[gerty]

Do you have room for a magnetic reed switch??

 

[ante]

Or maybe a Hall switch, no moving contacts!

 

[zevon8]

ante, gerty: hmmm... both good ideas. There is room for either. The big issue is getting the signal from the device, without having to worry about processing it, or noise being picked up. Vehicles can be a nightmare of electrical noise. I wonder if it would be possible to "focus" the magnetic viewing angle of either one? The only drawback I can think of right off hand would be false readings caused by the motors that are moving the machinery. The hall sensor would perhaps be the easiest to focus, but the reed switch easier to deploy. Either switch could be shielded nearly all the way around, leaving only a small window for magnetic flux.

The beauty of the mercury switch design was the simplicity... one side grounded or at 12VDC, the other the signal wire, so the system was basically one wire.

But using the Hall or reed switch may also be a winner! Micronas HAL55x series might be good for this. A transitor as a gate could sense the current differential of the Hall device. Probably need to use shielded wire. I will have to experiment and see

Thanks for the input!

 

[Oznog]

But using the Hall or reed switch may also be a winner! Micronas HAL55x series might be good for this. A transitor as a gate could sense the current differential of the Hall device. Probably need to use shielded wire. I will have to experiment and see

Thanks for the input!

You could also perhaps use an infrared photodetector. It's a bit hard to make it work if exposed to direct sunlight, and susceptible to dirt, but otherwise pretty effective.

The Hall effect switch is a good idea. A reed switch is mechanical and subject to wear and mechanical failure. Enough vibration can cause those thin reeds to contact momentarily too.

 

[zevon8]

One experiment done. Test drove the reed switch ( literally. ) It's a no-go. Lots of erratic behaviour. Tried rotating it axially, pretty much the same results. Doesnt have the inertial of the mercury, so the contacts bounce together. The mercury will do this too, but not very often. You don't realize how harsh a vehicles chassis rides until you do stuff like this. :shock:

It's Hall sensor test time now.

Oznog: the photodetector could work mechanically, but you're right, I think keeping it clean would be hard. Too much road dirt, salt spray ( in winter ), etc.

 

[Nigel Goodwin]

It's Hall sensor test time now.

As a hall sensor has no moving parts (and assuming both the sensor and magnet are securely fixed), it should cure all your 'bounce' problems.

 

[captainkirksdog]

Hola!
Try using a metal-can style of mercury switch. You can sometimes find them in small ceramic space heaters for anti-tip-over protection. They are rugged, self-contained (no glass envelope to break), and should be still available. Good luck!

 

[zevon8]

captainkirksdog: metal-can style of mercury switch

True, they are very durable, and they are a good choice for ruggedness. The problem ( other than durability with the glass package ) is the mercury. WEEE and RoHS rules are making it very difficult to use mercury in products. Right now I can label the switch, and protect it from accidental spillage, but soon I won't be able to use mercury at all.

Thanks for the idea though!

 

[dingo]

Is this 90 Deg in relation to ground or gravity? Reason i'm asking is a tilt switch out of a pin ball machine would be perfect if gravity. Might even work if ground, if you don't park on real steep hills and your 90 deg does not need to be exact.

 

[dingo]

Home made pinball tilt switch. You will not be able to break this easy and will only need one wire.

 

[zevon8]

Hi all, late reply due to field service work. Thanks for the idea dingo, but the environment of the application would ruin that type of switch in fairly short order. The mode of operation is 90 degrees from level, deflected by gravity.

It has been accepted by the customer that mercury switches are OK at the moment as long as they are labeled as such. Probably I will use the metal envelope type, as suggested by captainkirksdog, I have found a suitable supply.

I think that in future designs, Hall effect will be the way to go, I have done some "crude" experimentation that shows this to be viable.

I really appreciate everyones efforts in this, thanks for contributing!

 

[tansis]

In your eagerness to comply with new enviromental regulations
are you confident your modification will not fall foul of existing
Health and Safety requirements.

machinery aboard a vehicle, operator unable to observe deployment, sounds bad enough, but what puzzles me is the phrase
"using a limit switch is not possible, due to the small size of the equipment being deployed, and various mechanical limitations"

It does sound like some kind of "homebrew" vehicle modification as opposed to something it left the factory with , rules for this vary around the world and would advise checking with local govt vehicle inspector.

 

[zevon8]

In your eagerness to comply with new enviromental regulations are you confident your modification will not fall foul of existing
Health and Safety requirements.

I understand what you are saying, and it does sound like this project is "bandaging" at the risk of making things worse. The equipment is from the customer, and meets all of their requirements for regulations, this is merely an added feature they asked us to incorporate.

machinery aboard a vehicle, operator unable to observe deployment, sounds bad enough, but what puzzles me is the phrase
"using a limit switch is not possible, due to the small size of the equipment being deployed, and various mechanical limitations"

The equipment is on the roof of a large cube-van, so it is not possible to see it from inside the vehicle, and you would need to be several metres away from the vehicle to see it while standing on the ground. The mechanical limitations are the result of the way the equipment colapses in onto itself. Think along the lines of a small telescoping arm that folds into a recess when closed. The vehicle it is mounted on is kept in a building with a rollup door that just clears the roof of the van, so the operator needs to be sure that the device is down and stowed properly before driving into the building.

It does sound like some kind of "homebrew" vehicle modification as opposed to something it left the factory with , rules for this vary around the world and would advise checking with local govt vehicle inspector.

This is a municipal utility works department truck, the only things that it left the factory with are the chassis and the cab. It has everything from diesel generators to a microwave oven ( so the crew can eat while staying at a worksite )

Don't get me wrong, I appreciate your input and agree the whole thing sounds weird. It's one of those challenges you have to see to believe. The project started with operators wishing they had a simple way to tell if the equipment was actually down so they could drive into the garage without ripping the thing off the roof or causing damage. Once the proposed solution was presented, the fact mercury was involved raised the ire of the Health and Safety people. Being a government controlled entity, they have strict hazmat rules. We have to provide MSDS sheets for all materials and products that are used in everything we build for this customer.

Ah the joys of red tape

 

[tansis]

having driven off with the roof of my old bedford cf camper van
still erected on more than one occasion i understand only to well

i guess it is one of those problems that has to been seen first hand
in order to comprehend just how awkward a simple request can be to implement in practise.

my own brother has a similiar request for me to build a 'pop up'
air scoop into the bonnet/ hood of his car.